Plant-based expression systems have been increasingly used in producing proteins, because of a variety of advantages over the conventional expression system in bacterial or animal cells. For example, plants are capable of producing proteins in a large scale at low cost, plants do not contain animal pathogens that may cause contamination in the final protein product, and plant cells provide eukaryotic post translational processing that may be necessary for proper biological function of proteins. Examples of recombinant proteins that have been produced in plants include therapeutic proteins such as insulin, interferons, epidermal growth factors and immunoglobulins and industrial enzymes such as xylanase.
A promoter is a sequence of DNA that can initiate the transcription of a gene. A number of promoters which are active in plant cells have been described in the literature, including the cauliflower mosaic virus (CaMV) 35S promoter, the commelina yellow mottle virus promoter, the rice cytosolic triosephosphate isomerase (TPI) promoter, the rice actin 1 (Act1) gene promoter, the uniquitin (Ubi) promoter, the rice amylase gene promoter, the adenine phosphoribosyltransferase (APRT) promoter of Arabidopsis, the mannopine synthase and octopine synthase promoters.
There is a continue need for a modified promoter exhibiting strong activity for high-level expression of introduced genes, especially in plant cells.